This invention relates to an apparatus for validating a paper-like piece such as a bill or bank note, a note used as a substitute for money, a gift card, or a bill made of plastics and a collation method in such apparatus and, more particularly, to such apparatus and method capable of performing accurate validation and collation taking into account errors present in individual parts of an optical sensor or in assembling of these parts.
In this specification, the term "a paper-like piece" means a paper-like piece having a face value or identifying function such as a bill or bank note made of paper or plastics, a note used as a substitute for money, a gift card or an identification certificate.
As a sensor used in known validators, there is an optical sensor including a light-emitting element and a light-receiving element. In this type of optical sensor, a bill is passed, for example, between the light-emitting element and the light-receiving element and the amount of transmitted light corresponding to the design on the bill is detected, and the pattern on the bill is collated on the basis of the detected amount of transmitted light to validate the bill. There is also proposed a method of detecting the amount of reflected light in accordance with the pattern on the bill. As examples of such prior art optical type bill validator or bill validating method, there are publications including Japanese Patent Publication No. 41-20245, Japanese Utility Model Publication No. 43-23522, Japanese Patent Publication No. 53-39151, Japanese Patent Application Laid-open No. 54-5496 and Japanese Patent Application Laid-open No. 60-61883.
Japanese Patent Publication No. 41-20245 and Utility Model Publication No. 43-23522 disclose a general art of validating a bill by comparing a received light signal corresponding to the pattern of the bill with a predetermined reference pattern. Japanese Patent Publication No. 53-39151, Patent Application Laid-open No. 54-5496, Patent Application Laid-open No. 60-61883 and others disclose a technique for coping with variation in the received light level occurring due to variations in the measuring conditions which are resultant from aging and thermal property of the light-emitting and light-receiving elements and deposition of soil on a bill.
A typical example of the prior art for coping with variation in the received light level due to variations in measuring conditions is a method according to which the received light signal level in a stand-by mode (i.e., a mode in which a bill has not been inserted in the validator) is measured, and then a pattern of a bill is normalized on the basis of the measured value. In other words, reference pattern data is prepared in the form of a ratio of a received light signal level corresponding to a detected pattern, to a received light signal level in the stand-by mode. The received light signal level in the stand-by mode (current stand-by mode level) is measured at each occasion of detection, then a received light signal level corresponding to the pattern of an inserted bill which is measured at each occasion of detection is converted to the ratio to the current stand-by mode level and this ratio is compared with the reference pattern data. In short, the received light signal level which is an absolute value is converted to a relative value based on the stand-by mode for collation.
In the above described prior art method, no serious problem arises in cases where a high degree of accuracy of validation is not required. In a case where a high degree of accuracy of validation is required, however, the following problem will arise. In a case, for example, where a magnetic validation device performing validation by detecting a magnetic component in printing ink is provided in addition to the optical type validation device for improving the accuracy of validation, the accuracy of validation by the optical validation device per se may be relatively rough. In a case where no magnetic component exists in the printing ink, however, there is no means for improving the accuracy of validation but performing an accurate validation with the use of the optical type validation device and, accordingly, a high degree of accuracy of validation by the optical type validation device per se is required.
A problem caused by the optical type validation device is a problem caused by a parts error and an assembling error of the optical sensor. The parts error is an error in individual elements such as a light-emitting element and a light-receiving element which are used as parts of an optical sensor. Even if each part is made so as to satisfy a certain standard, there is an irregularity between individual elements within the standard. Accordingly, the amount of emitted light may differ from element to element even if the same input electrical signal is given, or output electrical signals may differ even if the same amount of light is received, or the irradiation field pattern of the light-emitting element may differ from element to element. This is the parts error. The assembling error is an irregularity in the accuracy of assembling of parts of an optical sensor, that is, the relation between the irradiation field of the light-emitting element and the position of the light-receiving element differs slightly from one optical sensor to another due to irregularity in assembling of the parts.
FIGS. 12a-12c show, as an example of the parts error, irregularities between the irradiation field patterns of individual light-emitting elements. FIG. 12a shows an example in which located in the center of a bright circle. FIG. 12b shows an example in which a half-bright spot is located in the center of a bright circle and further a bright spot is located in the center of the half-bright spot. FIG. 12c shows an example in which a half-bright spot is located at a position slightly offset from the center of a bright circle.
FIGS. 13a and 13b show, as an example of the assembling error, irregularities in the locational relations between irradiation fields L1 and L2 of a light-emitting element and position R of a light-receiving element. L1 denotes a bright circle and L2 a half-bright spot. FIG. 13c shows an example in which there is substantially no assembling error with respect to irradiation field L1, but position R of a light-receiving element with respect to irradiation fields L1 and L2 is offset due to offsetting of the irradiation field L2 with respect to the irradiation field L1.
Such parts and assembling errors adversely affect the output signal level of a light-receiving element. This effect is relatively small when received light is in a saturated or nearly saturated state but becomes remarkable in a moderate light receiving state corresponding to the pattern on a bill.
FIG. 14 shows an example of a light-receiving element's output signal in a light transmitting system. In the stand-by mode, the received light is in a saturated state and the light-receiving element's output signal level is at the maximum. When a bill is passing through an optical sensor, light is interrupted and the light-receiving element output signal level therefore drops and there arises variation in the light-receiving element's output signal level corresponding to the pattern of the bill. By comparing and collating the variation pattern of this light-receiving element's output signal level during passing of the bill with a predetermined reference pattern, the inserted bill is validated. In the figure, solid line X shows an example of a light-receiving element's output signal of a certain apparatus and dotted line Y shows an example of a light-receiving element output signal of another apparatus concerning the same bill. The light-receiving element output signal level differs depending upon the parts error and assembling error in an optical sensor in each apparatus. For example, the light-receiving element output signal level in the stand-by mode is T10W in the solid line X whereas it is T20W in the dotted line Y. The light-receiving element's output signal level during passing of the bill also differs between the solid line X and the dotted line Y. For example, at a point A, the signal level is T10a in the solid line X but it is T20a in the dotted line Y.
The ratio of the light-receiving element's output signal level during passing of the bill to the light-receiving element's output signal level in the stand-by mode at the point A is T10a/T10W in the solid line X and T20a/T20W in the dotted line Y. Owing to difference between T10W and T20W and difference between T10a and T20a, values of the respective ratios are different from each other. If, therefore, common reference pattern data is used, there arises the problem that an accurate validation cannot be performed.
Even if the value of reference pattern data is changed for each apparatus, the conventional normalizing method of obtaining a ratio of the light-receiving element's output signal level during passing of the bill to the light-receiving element's output signal level in the stand-by mode has the problem that the parts and assembling errors affect the accuracy adversely, because one of the output signal levels is a saturated value and the other is an unsaturated value so that difference between the two values is large, thus with a resulting small value of ratio making it difficult to perform an accurate validation, and, further because the effect of the parts and assembling errors is relatively small in the saturated value whereas this effect is remarkable in the unsaturated value. Further, aging due to soil or deterioration of the sensor affects the difference or ratio between the saturated value and the unsaturated value caused by the parts and assembling errors, which becomes one of the reasons for inability of the conventional method to improve the accuracy in validation.